The transient receptor potential (TRP) channels or receptors are increasingly recognized as transducers of pain signal in response to mechanical, thermal, inflammatory and chemical assaults. They have been classified into seven subfamilies: TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin), TRPML (mucolipin), TRPA (ankyrin, ANKTM1) and TRPN (NOMPC) families. The TRPC sub-family are the original members which were discovered and are homologous to the Drosophila trp-channel. Seven isoforms (TRPC1-TRPC7) have been characterized so far. Currently the TRPV family has 6 members. TRPVS and TRPV6 are more closely related to each other than to TRPV1, TRPV2, TRPV3 or TRPV4. TRPA1 is most closely related to TRPV3 and is more closely related to TRPV1 and TRPV2 than to TRPVS and TRPV6. The TRPM family has 8 members. Constituents include the following: the founding member TRPM1 (melastatin or LTRPC1), TRPM3 (KIAA1616 or LTRPC3), TRPM7 (TRP-PLIK, ChaK(1), LTRPC7), TRPM6 (ChaK2), TRPM2 (TRPC7 or LTRPC2), TRPM8 (TRP-p8 or CMR1), TRPMS (MTR1 or LTRPCS) and TRPM4 (FLJ20041 or LTRPC4). The TRPML family consists of the mucolipins, which include TRPML1 (mucolipin 1), TRPML2 (mucolipin 2) and TRPML3 (mucolipin 3). The TRPP family consists of two groups of channels: those predicted to have six transmembrane domains such as TRPP2 (PKD2), TRPP3 (PKD2L1), TRPP5 (PKD2L2) and those that have eleven domains such as TRPP1 (PKD1, PC1), PKD-REJ and PKD-1L1. The sole mammalian member of the TRPA family is ANKTM1.
It is believed TRPA1 is expressed in nociceptive neurons. Nociceptive neurons of the nervous system sense the peripheral damage and transmit pain signals. TRPA1 is membrane bound and most likely acts as a heterodimeric voltage gated channel. It is believed to have a particular secondary structure, its N-terminus is lined with a large number of ankyrin repeats which are believed to form a spring-like edifice. TRPA1 is activated by a variety of noxious stimuli, including cold temperatures (activated at 17° C. and below), pungent natural compounds (e.g., mustard, cinnamon and garlic) and environmental irritants (MacPherson L J et al, Nature, 2007, 445; 541-545). Noxious compounds activate TRPA1 ion channels through covalent modification of cysteines to form covalently linked adducts. Variety of endogenous molecules produced during inflammation/tissue injury or allergy have been identified as pathological activators of TRPA1 receptor. These include hydrogen peroxide which is produced due to oxidative stress generated during inflammation, alkenyl aldehyde 4-HNE—an intracellular lipid peroxidation product and cyclopentenone prostaglandin 15dPGJ2 which is produced from PGD2 during inflammation/allergic response. TRPA1 is also activated in receptor dependant fashion by Bradykinin (BK) which is released during tissue injury at peripheral terminals.
The difference between TRPA1 and other TRP receptors is that TRPA1 ligand binding persists for hours due to which the physiological response (e.g., pain) is greatly prolonged. Hence to dissociate the electrophile, an effective antagonist is required.
In efforts to discover better analgesics for the treatment of both acute and chronic pain and to develop treatments for various neuropathic and nociceptive pain states, there exists a need for a more effective and safe therapeutic treatment of diseases, conditions and/or disorders modulated by TRPA1.
International publications WO2010109287, WO2010109328, WO2010109329 and WO2010109334, WO2009118596, WO2009144548, WO2010004390, IN200802512, WO2010125469, WO2011114184, WO2011132017, WO2007073505, WO2010075353, WO2009158719, WO2009002933 and WO2010132838 disclose various 2-amino-4-arylthiazole compounds which are useful for treating disorders related to TRPA1.
It has been found that a few of the 2-amino-4-arylthiazoles compounds having high TRPA1 activity are characterized by low aqueous solubility which may contribute to poor pharmacokinetic properties. Therefore it is important to find ways to improve the solubility and pharmacokinetic profile of these compounds.
Therefore it is an object of the present application to provide 2-amino-4-arylthiazole compounds having improved solubility and/or pharmacokinetic properties.